The behavior and functionality of semiconductor heterojunctions depend critically on the alignments of the valence and conduction bands at the various interfaces. Traditionally, band alignment has been measured by x-ray photoelectron spectroscopy using pairs of distinct core levels, one from each side of the interface, to track the valence band maxima in the two materials. Here, we demonstrate that band alignment across an interface can also be determined using a single core-level photoelectron spectrum for an element that is common to both materials. The energy splitting between the photoemission features originating in the two materials is shown to be dominated by the difference in electrostatic potential across the interface, thereby leading to a reliable determination of the band alignment.

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